The present invention relates to an optical component having an optical surface molded by using a mold, a method of molding an optical component, and a mold for an optical component.
A mold can manufacture an optical component having a specific surface such as an aspherical surface with good productivity and at a low cost. By using this advantage, such an optical component is conventionally formed by using a mold. An example of such an optical component includes a lens for an optical scanning system, e.g., a laser printer or digital copying machine, or for a reading optical system, e.g., a facsimile apparatus or copying machine; and a lens, a mirror, a prism, and the like for a mirror image sensing optical system, a finder optical system, and an auto-focus optical system.
To mold an optical component by using, e.g., a plastic, a mold 101 as shown in FIG. 14 is used to obtain a molded product 102 as shown in FIG. 15. The molded product 102 is cut at its gate molding portion 103 to obtain, in the example of FIG. 15, a meniscus convex lens 105 having a flange 104 as an optical component.
A stationary side template 107 is attached to a stationary side mounting plate 106 of the mold 101 connected to an injection apparatus (not shown). A movable side template 109 for forming a cavity 108 corresponding to the meniscus convex lens 105 together with the stationary side template 107 is fixed to a movable side mounting plate 112 through a pressure spacer 110 and a spacer block 111. An ejector plate 113 is accommodated between the pressure spacer 110 and movable side mounting plate 112 connected to a mold locking apparatus (not shown), and is movable toward the stationary side template 107. Ejector pins 114 extend from the ejector plate 113 to be slidable through the pressure spacer 110 and movable side template 109. The distal end faces of the ejector pins 114 oppose a cavity (this constitutes the peripheral portion of the cavity 108 of the meniscus convex lens 105 and will be referred to as the second cavity hereinafter to distinguish it from the cavity 108 having an optical surface) 115 and a sprue 116.
The mold 101 is adjusted to a predetermined temperature. Molten plastic is supplied from the injection apparatus to the mold 101 through the sprue 116 formed in the stationary side mounting plate 106 and template 107, and flows through a runner 117 and a gate 118 to fill the cavity 108 through the second cavity 115. After that, the plastic in the cavity 108 is cooled, the movable side template 109 is separated from the stationary side template 107, and the ejector plate 113 is moved forward toward the stationary side template 107, so that the molded product 102 shown in FIG. 15 is ejected from the movable side template 109 through the ejector pins 114.
In addition to the gate molding portion 103 described above, the meniscus convex lens 105 having the flange 104 of the molded product 102 is integrally formed with a runner molding portion 119 and a sprue molding portion 120 continuous to the gate molding portion 103. When the molded product 102 is cut at its gate molding portion 103, the meniscus convex lens 105 having the flange 104 can be obtained.
When the meniscus convex lens 105 is to be obtained from the molded product 102 as shown in FIG. 15, conventionally, an outer appearance defect called a weld is sometimes formed on the surface of a convex optical surface 121 of the meniscus convex lens 105 close to the gate molding portion 103. How the weld is formed will be described with reference to FIGS. 16 and 17.
FIGS. 16 and 17 show how molten plastic 122 flows from the gate 118 to the cavity 108 through the second cavity 115. When the molten plastic 122 is molded using the mold 101 shown in FIG. 14, it is cast into the cavity 108 through the sprue 116, runner 117, and gate 118. Conventionally, the runner 117, gate 118, and second cavity 115 are linear, i.e., are linearly aligned in a direction perpendicular to the optical axis of the meniscus convex lens 105. As shown in FIG. 16, the molten plastic 122 entering the second cavity 115 comes into contact with a concave optical surface molding surface 123 of the cavity 108 and then flows into the cavity 108 along the concave optical surface molding surface 123. After the molten plastic 122 fills the cavity 108 to a certain degree, as shown in FIG. 17, the molten plastic 122 flowing along the concave optical surface molding surface 123 extends to come into contact with a convex optical surface molding surface 124 corresponding to the convex optical surface 121 at a portion indicated by an arrow A in FIG. 17. At this time, this portion of molten plastic 122 overlaps a distal end portion B of its another portion which flows along the convex optical surface molding surface 124 from the beginning.
In this case, the molten plastic 122 flowing along the concave optical surface molding surface 123 to come into contact with the convex optical surface molding surface 124 at the portion indicated by the arrow A and the molten plastic 122 flowing along the convex optical surface molding surface 124 from the beginning are deprived of heat by the stationary and movable side templates 107 and 109, and their viscosity has accordingly increased. For this reason, at a portion indicated by an arrow C, these two flows of the molten plastic 122 do not merge but form a thin parting line. This parting line is the weld.
More specifically, referring to FIG. 16, when molding is to be performed by using the mold 101, flange portions which continue from the concave optical surface molding surface 123 with a size D2 and have sizes D1 and D3 are formed, so that a line segment L1 as a tangent to the curvature of the cavity portion that molds the concave optical surface molding surface 123 makes an angle .alpha. of 15.degree. or more with a line segment L2 extending from the flange portion. Since the flange and gate portions are linear, i.e., linearly aligned in a direction perpendicular to the optical axis of the meniscus convex lens 105, the weld described above is formed.